During drilling operations, drilling fluid is pumped down the drill string. The drilling fluid serves to carry cutting from the drill bit to the surface and creates a hydrostatic pressure that prevents a blowout condition from occurring. The drill string consists of a plurality of joined sections of pipe. As these joined sections of pipe are "tripped" out of the hole they must be disconnected. When they are disconnected drilling fluid tends to spray uncontrollably over men and equipment. U.S. Pat. No. 319,693 which issued in 1932 describes an apparatus which was developed to disconnect sections of drill string. This apparatus, which is still in use today, has come to be known as a "mud saver". It consists of cooperating semi-circular wall members which fit around a joint to form an enclosed chamber. In order to provide pressure containment the apparatus weighs approximately 500 pounds and is suspended in position by a hoist while two or more men swing it in and out of position. The pipe joint is disconnected while inside the enclosed chamber. The drilling fluid which is released is drained by a drainage member, usually in the form of a flexible hose. The use of this apparatus helps prevent the derrick floor from becoming slippery with drilling fluids. It also prevents the loss of drilling fluids which could otherwise be recirculated.
A kelly and its associated rotary hose contain approximately 20 gallons of drilling fluid. When the kelly is disconnected from the drill string that drill fluid exits under considerable pressure. The problems associate with the disconnection of the kelly are similar to the problems encountered when disconnecting the joints of drill pipe making up the drill string. However apparatus, such as described in U.S. Pat. No. 319,693, are unsuitable for use when disconnecting the kelly as the Kelly bushing is in the way.
Another approach that has been used to address the problem is to attach a valve directly to the Kelly, with the valve becoming part of the drill string. An example of such a valve is U.S. Pat. No. 3,738,436 which issued to Smith International Inc. in 1973. The reference discloses a valve which closes when drill pipe pressures decrease below preset levels. When the valve is in the closed position, drilling fluid is contained within the Kelly. The valves are in constant communication with abrasive drilling fluids. Maintenance is required on a weekly or bi-monthly basis to avoid valve failure.